As a pioneering Professor at a prestigious university, Meitner was at the forefront of her field, both socially (as a woman) and scientifically (at the cutting edge of technology and technique). From the 1920s to 1934, Meitner's Physics department and Hahn's Chemistry department worked separately, though collaboration was frequent.

After a study of Protactinium, Meitner began work on the relationship between beta and gamma radiation (beta radiation is the emission of an electron from the nucleus when a neutron decays into an electron, a positron and a neutrino. Gamma radiation is when a nucleus emits excess energy as a ray). This led, in 1925, to the realisation that electron lines were emitted before and not after radioactive transformation, contrary to scientific opinion of the time.

Meitner was also a pioneer of the use of the Geiger counter in nuclear research, using them to test the passage of gamma rays through matter (a gamma ray, unlike alpha or beta particles, has great penetrative power).

In 1934, following Fermi's experiments on neutron bombardment in Rome, Hahn and Meitner's collaboration became more direct. Following the discovery of the neutron in 1932 by Chadwick, Meitner was enthusiastic about the new developments in nuclear physics. Fermi's experiments showed that when a heavy element is bombarded with neutrons, a heavier isotope of that element is formed. Fermi's explanations of this were at best vague and forced.

Meitner, Hahn and a new collaborator, Fritz Strassman (1902 - 1980) set to work replicating and expanding upon these original experiments of Fermi's. However, in 1938, when the German army entered Austria, it was no longer possible for Meitner (a Jew by descent, but not practise) to remain in Berlin. She fled to Sweden in July, aided by Niels Bohr.